Her brother, Nagaenthran Dharmalingam, is set to be hanged in Singapore's Changi Prison. If it happens, it will be the first execution Singapore has carried out since 2019.
"When I'm alone and I think of my brother, there is pain. But [we need to] be brave and keep on praying - anything can happen," she told the BBC.
Nagaenthran is due to be hanged on Wednesday morning, but was granted a last-minute stay of execution for a day. A court of appeal will decide his fate on Tuesday.
In 2009, then 21-year-old Nagaenthran was found trying to smuggle heroin into Singapore from Malaysia.
The Malaysian citizen was sentenced to death despite an assessment by a medical expert that he has an IQ of 69 - a level recognised as indicating an intellectual disability.
But the Singapore government said he was found to have "clearly understood the nature of his acts and did not lose his sense of judgment of the rightness or wrongness of what he was doing".
Photo file Caption: Nagaenthran Dharmalingam faces execution in Singapore for trying to smuggle heroin from Malaysia